Polymorphism, distribution, and segregation of AFLP markers in a doubled haploid rice population

We exploited the newly developed amplified fragment length polymorphism (AFLP) technique to study the polymorphism, distribution and inheritance of AFLP markers with a doubled haploid rice population derived from ‘IR64’/‘Azucena’. Using only 20 pairs of primer combinations, we detected 945 AFLP bands of which 208 were polymorphic. All 208 AFLP markers were mapped and distributed over all 12 chromosomes. When these were compared with RFLP markers already mapped in the population, we found the AFLP markers to be highly polymorphic in rice and to follow Mendelian segregation. As linkage map of rice can be generated rapidly with AFLP markers they will be very useful for marker-assisted backcrossing. Received: 11 April 1996 / Accepted: 14 June 1996     

Genetic analysis of adult plant,quantitative resistance to stripe rust in wheat cultivar ‘Stephens’ in multi-environment trials

The wheat (Triticum aestivum L.) cultivar ‘Stephens’ has been grown commercially in the USA Pacific Northwest for 30 years. The durable resistance of ‘Stephens’ to stripe rust (Puccinia striiformis f. sp. tritici) was believed to be due to a combination of seedling and adult plant resistance genes. Multilocation field trials, diversity array technology (DArT), and simple sequence repeat (SSR) markers were used to identify quantitative trait loci (QTL) for resistance. Recombinant inbred lines were assessed for stripe rust response in eight locations/years, five in 2008 and three in 2009. The data from Mt. Vernon, WA, differed from all other environments, and composite interval mapping (CIM) identified three QTL, QYrst.orr-1AL, QYrst.orr-4BS, and QYrpl.orr-6AL, which accounted for 12, 11, and 6% of the phenotypic variance, respectively. CIM across the remaining six environments identified four main QTL. Two QTL, QYrst.orr-2BS.2 and QYrst.orr-7AS, were detected in five of six environments and explained 11 and 15% of the phenotypic variance, respectively. Two other QTL, QYrst.orr-2AS and QYrpl.orr-4BL, were detected across four and three of six environments, and explained 19 and 9% of the phenotypic variance, respectively. The susceptible parent ‘Platte’ contributed QYrpl.orr-4BL and QYrpl.orr-6AL, with the remaining QTL originating from ‘Stephens’. For each environment, additional minor QTL were detected, each accounting for 6–10% of the phenotypic variance. Different QTL with moderate effects were identified in both ‘Stephens’ and ‘Platte’. Significant QTL × environment interactions were evident, suggesting that specificity to plant stage, pathogen genotype, and/or temperature was important.     

Cloning and characterisation of a family of disease resistance gene analogs from wheat and barley

 The most common class of plant disease resistance (R) genes cloned so far belong to the NBS-LRR group which contain nucleotide-binding sites (NBS) and a leucine-rich repeat (LRR). Specific primer sequences derived from a previously isolated NBS-LRR sequence at the Cre3 locus, which confers resistance to cereal cyst nematode (CCN) in wheat (Triticum aestivum L.) were used in isolating a family of resistance gene analogs (RGA) through a polymerase chain reaction (PCR) cloning approach. The cloning, analysis and genetic mapping of a family of RGAs from wheat (cv ‘Chinese Spring’) and barley (Hordeum vulgare L. cvs ‘Chebec’ and ‘Harrington’) are presented. The wheat and barley RGAs contain other conserved motifs present in known R genes from other plants and share between 55–99% amino acid sequence identity to the NBS-LRR sequence at the Cre3 locus. Phylogenetic analysis of the RGAs with other cloned R genes and RGAs from various plant species indicate that they belong to a superfamily of NBS-containing genes. Two of the barley derived RGAs were mapped onto loci on chromosomes 2H (2), 5H (7) and 7H (1) using barley doubled haploid (DH) mapping populations. Some of these loci identified are associated with regions carrying resistance to CCN and corn leaf aphid. Received: 6 January 1998 / Accepted: 1 April 1998     

Genetic studies of Triticeae dehydrins: assignment of seed proteins and a regulatory factor to map positions

 A collection of 200 wheat (Triticum aestivum L. cv ‘Chinese Spring’) cytogenetic stocks (nullisomic, tetrasomic, nulli-tetrasomic, ditelosomic and deletion lines, addition and substitution stocks from intra- and inter-specific crosses) was utilized to determine the proteins encoded by some of the wheat and barley dehydrin genes, using a western blot procedure. Proteins extracted from seeds were reacted with antibodies that recognize dehydrins in a wide range of plants, including wheat and barley. Proteins encoded by dehydrin loci in chromosome arms 4DS, 5BL and 6AL of ‘Chinese Spring’ wheat were assigned by this method. There was also evidence of a regulatory factor on 5B in the vicinity of the dhn genes, and on 5H in wheat-barley addition lines, that is required for a normal level of expression of seed dehydrins in hexaploid wheat. Further understanding of this putative regulatory factor would be helpful for the interpretation of linkage studies that may relate dehydrin gene expression to phenotypes such as dehydration, salinity or low-temperature tolerance. Received: 27 August 1997 / Accepted: 4 February 1998     

Resistance gene analogues from rice: cloning, sequencing and mapping

 Degenerate oligonucleotide primers were designed on the basis of nucleotide-binding-site (NBS) motifs conserved between resistance genes of Arabidopsis, flax and tobacco and subsequently used as PCR primers to amplify resistance gene analogues (RGA) in rice. Primers amplified a major band of approximately 500 bp. Restriction analysis of the amplified product revealed that the band was made up of several different fragments. Many of these fragments were cloned. Sixty different cloned fragments were analysed and assigned to 14 categories based on Southern blot analysis. Fourteen clones, each representing one of the 14 categories of RGAs were mapped onto the rice genetic map using a Nipponbare ( japonica)בKasalath’ (indica) mapping population consisting of 186 F₂ lines. Of the 14 clones representing each class 12 could be mapped onto five different chromosomes of rice with a major cluster of 8 RGAs on chromosome 11. Our results indicate that it is possible to use sequence homology from conserved motifs of known resistance genes to amplify candidate resistance genes from diverse plant taxa. Received: 23 September 1998 / Accepted: 28 November 1998     

PCR-based DNA markers linked to a gall midge resistance gene, Gm4t, has potential for marker-aided selection in rice

Rice DNAs from a gall midge resistant variety, Abhaya, a susceptible variety, Tulsi and their F₃ progeny were screened using 500 random primers in conjunction with bulked-segregant analysis in a polymerase chain reaction (PCR) with a view to detecting random amplified polymorphic DNAs (RAPDs) linked to the gene, Gm4t, which confers resistance to gall midge, a dipteran insect pest of rice. A total of 454 primers were able to produce a distinct amplification pattern, and 3695 bands/loci were amplified between the phenotypically different parents. Of these, 304 bands were polymorphic between the parents, with 19 being phenotypespecific. One of these primers, E20, amplified 2 bands, E20₅₇₀ and E20₅₈₃, which are tightly linked to resistance and susceptibility, respectively. These specific bands were cloned and sequenced, and a 94% sequence homology was found between the two fragments. Two specific 20-mer oligonucleotides were synthesized, based on the sequence information of E20₅₈₃, for use in PCR amplification directly from genomic DNAs. These PCR primers were able to amplify phenotype-specific bands, a 583-bp fragment in susceptible F₃ lines and a 570-bp fragment in resistant F₃ lines that had been derived from a cross between the parents, indicating their potential and utility for marker-aided selection of the Gm4t gene in rice. Its use would facilitate the early and efficient selection of resistant genes in plant breeding programmes and even in those areas where the insect is not known to occur. These phenotype-specific bands are single-copy sequences and are being mapped to ascertain their chromosomal location in rice.     

A linkage map of the pea (Pisum sativum L.) genome containing cloned sequences of known function and expressed sequence tags (ESTs)

 A linkage map of the pea (Pisum sativum L.) genome is presented which is based on F₂ plants produced by crossing the marrowfat cultivar ‘Primo’ and the blue-pea breeding line ‘OSU442-15’. This linkage map consists of 209 markers and covers 1330 cM (Kosambi units) and includes RFLP, RAPD and AFLP markers. By mapping a number of anchor loci, the ‘Primo’בOSU442-15’ map has been related to other pea linkage maps. A feature of the map is the incorporation of 29 loci representing genes of known function, obtained from other laboratories. The map also contains RFLP loci detected using sequence-characterized cDNA clones developed in our laboratory. The putative identities of 38 of these cDNA clones were assigned by examining public-sequence databases for protein or nucleotide-sequence similarities. The conversion of sequence-characterized pea cDNAs into PCR-amplifiable and polymorphic sequence-tagged sites (STSs) was investigated using 18 pairs of primers designed for single-copy sequences. Eleven polymorphic STSs were developed. Received: 18 June 1997 / Accepted: 11 August 1997     

Development of simple sequence repeat markers specific for the Lr34 resistance region of wheat using sequence information from rice and Aegilops tauschii

Hexaploid wheat (Triticum aestivum L.) originated about 8,000 years ago from the hybridization of tetraploid wheat with diploid Aegilops tauschii Coss. containing the D-genome. Thus, the bread wheat D-genome is evolutionary young and shows a low degree of polymorphism in the bread wheat gene pool. To increase marker density around the durable leaf rust resistance gene Lr34 located on chromosome 7DS, we used molecular information from the orthologous region in rice. Wheat expressed sequence tags (wESTs) were identified by homology with the rice genes in the interval of interest, but were monomorphic in the ‘Arina’ × ‘Forno’ mapping population. To derive new polymorphic markers, bacterial artificial chromosome (BAC) clones representing a total physical size of ∼1 Mb and belonging to four contigs were isolated from Ae. tauschii by hybridization screening with wheat ESTs. Several BAC clones were low-pass sequenced, resulting in a total of ∼560 kb of sequence. Ten microsatellite sequences were found, and three of them were polymorphic in our population and were genetically mapped close to Lr34. Comparative analysis of marker order revealed a large inversion between the rice genome and the wheat D-genome. The SWM10 microsatellite is closely linked to Lr34 and has the same allele in the three independent sources of Lr34: ‘Frontana’, ‘Chinese Spring’, and ‘Forno’, as well in most of the genotypes containing Lr34. Therefore, SWM10 is a highly useful marker to assist selection for Lr34 in breeding programs worldwide.     

Map construction of sequence-tagged sites (STSs) in barley (Hordeum vulgare L.)

 In order to identify sequence-tagged sites (STSs) appropriate for recombinant inbred lines (RILs) of barley cultivars ‘Azumamugi’ × ‘Kanto Nakate Gold’, a total of 43 STS primer pairs were generated on the basis of the terminal sequences of barley restriction fragment length polymorphism (RFLP) clones. Forty one of the 43 primer pairs amplified PCR products in Azumamugi, Kanto Nakate Gold, or both. Of these, two showed a length polymorphism and two showed the presence or absence of polymorphism between the parents. PCR products of the remaining 37 primers were digested with 46 restriction endonucleases, and polymorphisms were detected for 15 primers. A 383.6-cM linkage map of RILs of Azumamugi×Kanto Nakate Gold was constructed from the 19 polymorphic STS primer pairs (20 loci) developed in this study, 45 previously developed STS primer pairs (47 loci), and two morphological loci. Linkage analysis and analysis of wheat-barley chromosome addition lines showed that with three exceptions, the chromosome locations of the STS markers were identical with those of the RFLP markers. Received: 4 August 1998 / Accepted: 8 October 1998     

Localization of the rice stripe disease resistance gene, Stv-bi, by graphical genotyping and linkage analyses with molecular markers

 We used graphical genotyping and linkage analyses with molecular markers to determine the chromosomal location of the rice stripe disease resistance gene, Stv-b ⁱ . The stripe resistance gene from the indica rice (Oryza sativa) cv ‘Modan’ was introgressed into several Japanese rice varieties. We found 4 RFLP markers in ‘Modan’, five susceptible parental rice varieties (‘Norin No. 8’, ‘Sachihikari’, ‘Kanto No. 98’, ‘Hokuriku No.103’ and ‘Koganebare’) and four resistant progeny varieties (‘St. No. 1’, ‘Aichi No. 6’, ‘Aoisora’ and ‘Asanohikari’). Graphical genotyping of the resistant progeny revealed a chromosomal segment ascribable to ‘Modan’ and associated with stripe resistance. The chromosomal segment from ‘Modan’ was located at 35.85 cM on chromosome 11. Linkage analysis using 120 F₂ individuals from a cross between ‘Koshihikari’ (susceptible) and ‘Asanohikari’ (resistant) revealed another 8 RFLP markers in the same chromosome. We performed a bioassay for rice stripe resistance in F₃ lines of the F₂ individuals using infective small brown planthoppers and identified an 1.8-cM segment harboring the rice stripe disease resistance gene, Stv-b ⁱ , between XNpb220 and XNpb257/ XNpb254. Furthermore, Stv-b ⁱ was linked by 0.0 cM to a RFLP marker, ST10, which was developed on the basis of the results of RAPD analysis. These DNA markers near the Stv-b ⁱ locus may be useful in marker-assisted selection and map-based cloning of the Stv-b ⁱ gene. Received: 26 September 1997 / Accepted: 4 November 1997     

Postulation of resistance genes to barley diseases in heterogeneous varieties

Resistance to causal agents of diseases is an important varietal characteristic that influences the management practice of crop plants and thus production costs of commodities. At present, almost all European barley varieties possess at least one major gene for resistance to powdery mildew. After hybridizing selected parental varieties, resistance genes often segregate in subsequent generations and, therefore, some varieties comprise lines that differ in the number or combinations of resistance genes. The objective of this research was to describe the various methods available for postulating resistance genes to pathogens in heterogeneous varieties using resistance to powdery mildew of barley as an example. Four spring barleys (‘Orbit’, ‘Malva’, ‘Tocada’ and CLE 233), and a six-row variety of winter barley, F 12872, were screened. For postulating resistance genes, several testing procedures and many Blumeria graminis f.sp. hordei isolates were used. Minimum amounts of seed were determined and different methods of obtaining homogeneous seed samples from heterogeneous varieties were compared. It was found that ‘Orbit’ and ‘Malva’ are composed of three and ‘Tocada’, CLE 233 and F 12872 of two lines with different resistances to powdery mildew. Problems of postulating resistance genes in heterogeneous varieties and the advantages of testing leaf segments instead of young plants are discussed.     

Anchor probes for comparative mapping of grass genera

 Comparative mapping of cDNA clones provides an important foundation for examining structural conservation among the chromosomes of diverse genera and for establishing hypotheses about the relationship between gene structure and function in a wide range of organisms. In this study, “anchor probes” were selected from cDNA libraries developed from rice, oat, and barley that were informative for comparative mapping in the grass family. One thousand eight hundred probes were screened on garden blots containing DNA of rice, maize, sorghum, sugarcane, wheat, barley, and oat, and 152 of them were selected as “anchors” because (1) they hybridized to the majority of target grass species based on Southern analysis, (2) they appeared to be low or single copy in rice, and (3) they helped provide reasonably good genome coverage in all species. Probes were screened for polymorphism on mapping parents, and polymorphic markers were mapped onto existing species-specific linkage maps of rice, oat, maize, and wheat. In wheat, both polymorphic and monomorphic markers could be assigned to chromosomes or chromosome arms based on hybridization to nullitetrasomic and ditelosomic stocks. Linkage among anchored loci allowed the identification of homoeologous regions of these distantly related genomes. Anchor probes were sequenced from both ends, providing an average of 260 bp in each direction, and sequences were deposited in GenBank. BLAST was used to compare the sequences with each other and with a non-redundant protein sequence database maintained at the European Molecular Biology Laboratory (EMBL). Of the anchor probes identified in this study 78% showed significant similarity to protein sequences for known genes with BLASTX scores exceeding 100. Received: 27 June 1997 / Accepted: 17 July 1997     

Analysis of hybrids of durum wheat with Thinopyrum junceiforme using RAPD markers

 The objective of this study was to detect the presence of alien chromatin in intergeneric hybrids of durum wheat (Triticum turgidum, 2n=4x=28; AABB genomes) with the perennial grass Thinopyrum junceiforme (2n=4x=28; J₁J₁J₂J₂) using RAPD markers. The first step was to identify amplification of species-specific DNA markers in the parental grass species and durum wheat cultivars. Initially, the genomic DNA of five grass species (Thinopyrum junceiforme, Th. bessarabicum, Lophopyrum elongatum, Leymus karataviensis and Elytrigia pycnantha) and selected durum cultivars (‘Langdon’, ‘Durox’, ‘Lloyd’, ‘Monroe’, and ‘Medora’) was screened with 40 oligonucleotide primers (nano-mers). Three oligonucleotides that amplified DNA fragments specific to a grass species or to a durum cultivar were identified. Primer PR21 amplified DNA fragments specific to each of the five durum cultivars, and primers PR22 and PR23 amplified fragments specific to each of the grass species. Intergeneric hybrids between the durum cultivars ‘Langdon’, ‘Lloyd’ and ‘Durox’ and Th. junceiforme, and their backcross (BC) progeny were screened with all 40 primers. Six primers amplified parent-specific DNA fragments in the F₁ hybrids and their BC₁ progeny. Three primers, PR22, PR23 and PR41, that amplified Th. junceiforme DNA fragments in both F₁ and BC₁ were further analyzed. The presence of an amplified 1.7-kb Th. junceiforme DNA fragment in the F₁ hybrids and BC₁ progeny was confirmed using Southern analysis by hybridization with both Th. junceiforme genomic DNA and Th. junceiforme DNA amplified with primer PR41. With the exception of line BC₁F₂ no. 5, five selfed progeny of BC₁ and a BC₂ of line 3 (BC₁F₂ no. 3בLloyd’) from a cross of ‘Lloyd’×Th. junceiforme showed the presence of the 1.7-kb DNA fragment. All selfed BC₁ and BC₂ lines retained the 600-bp fragment that was confirmed after hybridization with Th. junceiforme DNA amplified with primer PR22. Other experiments using RFLP markers also showed the presence of up to seven Th. junceiforme DNA fragments in the F₁ hybrids and their BC progeny after hybridization with Th. junceiforme DNA amplified with primer PR41. These studies show the usefulness of molecular markers in detecting alien chromatin/DNA fragments in intergeneric hybrids with durum wheat. Received: 21 November 1996 / Accepted: 21 March 1997     

Expression of an engineered cysteine proteinase inhibitor (Oryzacystatin-IΔD86) for nematode resistance in transgenic rice plants

 We have used a genotype-independent transformation system involving particle gun bombardment of immature embryos to genetically engineer rice as part of a programme to develop resistance to nematodes. Efficient tissue culture, regeneration, DNA delivery and selection methodologies have been established for elite African varieties (‘ITA212’, ‘IDSA6’, ‘LAC23’, ‘WAB56-104’). Twenty-five transformed clones containing genes coding for an engineered cysteine proteinase inhibitor (oryzacystatin-IΔD86, OC-IΔD86), hygromycin resistance (aphIV) and β-glucuronidase (gusA) were recovered from the four varieties. Transformed plants were regenerated from all clones and analysed by PCR, Southern and western blot. Detectable levels of OC-IΔD86 (up to 0.2% total soluble protein) in plant roots were measured in 12 out of 25 transformed rice lines. This level of expression resulted in a significant 55% reduction in egg production by Meloidogyne incognita. Received: 4 August 1997 / Accepted: 22 August 1997     

Comparative analyses of RFLP diversity in landraces of Triticum aestivum and collections of T. tauschii from China and Southwest Asia

 Chinese accessions of Triticum tauschii and T. aestivum L. from the Sichuan white (SW), Yunnan hulled (YH), Tibetan weedrace (TW), and Xinjiang rice (XR) wheat groups were subjected to RFLP analysis. T. tauschii and landraces of T. aestivum from countries in Southwest Asia were also evaluated. For T. tauschii, a west to east gradient was apparent where the Chinese accessions exhibited less diversity than those from Southwest Asia. Compared to the Southwest Asian gene pool, the Chinese T. tauschii was highly homogeneous giving a low frequency of polymorphic bands (16%) and banding patterns (1.33 per probe) with 75 RFLP probe-HindIII combinations. Accessions of T. tauschii from Afghanistan and Pakistan were genetically more similar to the Chinese T. tauschii than those from Iran. Of 368 bands found for 39 Chinese hexaploid wheat accessions with 63 RFLP probe-HindIII combinations, 28.3% were polymorphic with an average of 2.6 banding patterns per probe and 5.0 bands per genotype. The individual Chinese landrace wheat groups revealed less variation than those from Afghanistan, Iran, and Turkey. When classified into country based groups, however, the diversity level over all Chinese landraces was greater than that of some Southwest Asian landraces, especially those from Afghanistan and Iran . The XR wheat group was genetically distinct from the other three Chinese landrace groups and was more related to the Southwest Asian landraces. The TW group was genetically similar to, but more diverse than, the SW and YH groups. The Chinese landraces had a higher degree of genetic relatedness to the Southwest Asian T. tauschii, particularly to accessions from Iran, rather than to the Chinese T. tauschii. ‘Chinese Spring’ was most related to ‘Chengdu-guang-tou’, a cultivar from the SW wheat group. Received: 13 May 1997 / Accepted: 19 September 1997     

Comparative mapping of a gibberellic acid-insensitive dwarfing gene (Dwf2) on chromosome 4HS in barley

 We report the genetic mapping of Dwf2, a dominant gibberellic acid (GA₃)-insensitive dwarfing gene which has been previously described to cause a very short growth habit in barley (Hordeum vulgare) mutant ‘93/B694’. Using RFLP and microsatellite markers we performed segregation analysis in an F₂ population comprising 86 individuals developed from a cross of ‘93/B694’ (Dwf2) with ‘Bonus M2’ (dwf2). Dwf2 was mapped on the short arm of barley chromosome 4H proximal to microsatellite marker XhvOle (5.7 cM) and distal to RFLP marker Xmwg2299 (18.3 cM). The genetic localization of the Dwf2 gene at a homoeologous position to the multiallelic Rht-B1 and Rht-D1 loci in wheat suggests synteny of GA-insensitive dwarfing genes within the Triticeae. Moreover, the extremely prostrate growth habit exhibited in barley ‘93/B694’ (Dwf2) resembles that of wheat plants carrying the genes Rht-B1c (Rht3) or Rht-D1c (Rht10). Received: 1 July 1998 / Accepted: 17 September 1998     

Characterisation of type-I thionin loci from the A, B, D and R genomes of wheat and rye

 DNA sequences encoding type-I thionins were isolated from Triticum aestivum L. cv ‘Chinese Spring’ using PCR with consensus primers. Blunt-end cloning, sequencing and PCR-based chromosome assignment of these fragments uncovered the three orthologous sequences corresponding to the single-copy genes at the Pur-1 loci on each of the group-1 chromosomes. Comparison with two previously published cDNA sequences revealed the presence of two introns that contain most of the polymorphic nucleotide sites. The observed orthologous DNA sequence variation among Pur-1 loci, encoded by each of the A, B and D genomes, enabled us to establish interlocus relationships and to construct locus-specific primer sets. Analogously, the Pur-R1 sequence from rye was isolated, and a locus-specific primer pair was constructed as well. Hence, four locus-specific primer sets are now available as molecular markers for the homoeologous 1AL, 1BL, 1DL and 1RL chromosome arms. Amplification from several diploid and tetraploid wheat species showed that the primers can be used as molecular tools for studying wheat phylogeny. Received: 30 January 1997 / Accepted: 23 June 1997     

Detection of genetic variation among micropropagated tea [Camellia sinensis (L.) O. Kuntze] by RAPD analysis

Summary Randomly amplified polymorphic DNA (RAPD) techniques were applied to assess genetic instability among micropropagated tea [Camellia sinensis (L.) O. Kuntze] eultivar ‘T-78’. Out of 49 random 10-mer primers, 11 generated polymorphism in four out of 17 micropropagated plants and one mother plant. A total of 221 bands, ranging from 525 bp to 2.5 kb, were produced by the 49 primers. Twenty-four were polymorphic for those four plants. However, the remaining bands were monomorphic among all plants. Polymorphism among those four plants showed an identifical banding pattern suggesting the occurrence of a single mutation. Our results demonstrated that RAPD can be used successfully to determine the genetic instability among micropropagated plants which otherwise were morphologically indistinguishable.     

Development of sex-linked PCR markers for gender identification in Actinidia

 Two sex-linked random amplified polymorphic DNA (RAPD) markers identified from Actinidia chinensis were converted into sequence-characterised amplified regions (SCARs) for the large-scale screening of Actinidia breeding populations. Initial SCAR primers converted one RAPD (SmX) into a dominant marker, but the other (SmY), which was potentially more useful because of its linkage to the male determining ‘Y’ locus, failed to retain polymorphism. This difficulty was overcome by cloning and sequencing the alternate ‘allele’ from female plants, and then designing ‘allele’-specific primers that utilised nucleotide differences between the sexes. Using a quick squash-blot method of DNA extraction, the SCAR primers were tested in 120 A. chinensis plants to determine their gender. The system is now in use for large-scale screening of seedling populations in the Actinidia breeding programme. The sex-linked SCAR primers also functioned with plants from some other geographically separate accessions of A. chinensis and with plants in the closely related polyploid species A. deliciosa, but did not amplify a sex-linked band in more distantly related species of Actinidia. Received: 27 December 1997 / Accepted: 5 March 1998     

Effects of drought and salinity on some growth-contributing parameters in wheat and barley

Summary This study is mainly concerned with some parameters contributing to growth as indicators of difference in drought resistance and salt tolerance of wheat and barley cultivars. Parameters made use of are: transpiration efficiency (‘dry matter/transpiration’ ratio), ‘leaf/root’ ratio, chlorophyll content, chlorophyll stability to heat and anatomical modifications. The results revealed that transpiration efficiency is much higher in mexican ‘super-x’ wheat than in the egyptian ‘Giza-155’ cultivar under reduced soil water matric- or osmotic potentials. Chlorophyll content increased in super-x with decreasing soil water potential while chlorophyll heat stability decreased. The reverse is true in Giza-155 cultivar. Decreased leaf/root ratio in super-x is interpretted in favour of more beneficial water balance in this cultivar. Development of more sclerenchyma in its stems supports this judgement. Of barley cultivars tested, Borg El-Arab is favoured for drought resistance and Giza-117 for salt tolerance. re]19751014